Tufting machines preferably operate at relatively high speed with one or more reciprocating rows of needles cooperating with loopers or hooks to form loops or bights of yarn on the reverse side of a backing material penetrated by the needle. The needles, loopers or hooks, knives, and needle plate fingers between which needles pass in their reciprocating movements, must be aligned with precision and accurately and uniformly spaced from each other so that the bills of loopers and hooks pass closely adjacent to the needles for engaging and holding yarns and the needle plate fingers do not interfere with the travel of the needles, and the knives interface with hooks to provide cutting action. When manufacturing these gauge components and the supports which carry the gauge components, any error or tolerance in positioning the components may accumulate or be repeated across the width of the tufting machine, which may be as much as four meters. In order to provide greater consistency, gauge elements have been manufactured in modular components. In many cases, modular components are cast or permanently fixed within blocks that are then mounted to specified positions along gauge bars. Examples of such modules are shown in Neely, U.S. Pat. No. 5,295,450.
In fine gauge machines, the use of modular components has become particularly widespread. So long as the mounting positions are accurately located along the gauge bar, the use of small modular sets of gauge components helps avoid accumulated error, allows for accurate and rapid location of replacement modules upon gauge element breakage, and is believed to minimize twisting of gauge elements during high speed operation.
Apart from cast modules containing gauge elements including needle plate fingers, two other general alternative modular needle plate element designs have found general acceptance. The first, as reflected in FIG. 9 of Price, et al., U.S. Pat. No. 4,548,140, utilizes screws to lock the fingers in place within a module, and would be referred to as a screw lock type needle plate module. The sizes of the screw posts and screw heads have conventionally acted as a limit upon the range of gauges of needle plate fingers that might reasonably utilized in screw lock style needle plate modules. Accordingly, these modules have been most frequently used when the gauge of a tufting machine is between about one-eighth and one-fourth gauge (between 8 and 4 yarns per inch (2.54 cm) of width). An alternative configuration utilizing a top clamping plate to hold the needle plate fingers in place is depicted in FIG. 4 of U.S. Pat. No. 4,548,140. This configuration has been adapted for use in situations in which the gauge of the tufting machine elements is to be outside the range of one-eighth to one-fourth gauge.
Thus, although the screw lock type needle plate block is desirable, until the present invention, no such construction had been developed that was deemed acceptable outside the one-eighth to one-fourth gauge range.